diff --git a/docs/agents.md b/docs/agents.md
index 3c6b1a6ef4..fb40341484 100644
--- a/docs/agents.md
+++ b/docs/agents.md
@@ -904,14 +904,15 @@ You should use:
 
 In general, we recommend using `instructions` instead of `system_prompt` unless you have a specific reason to use `system_prompt`.
 
-Instructions, like system prompts, fall into two categories:
+Instructions, like system prompts, can be specified at different times:
 
 1. **Static instructions**: These are known when writing the code and can be defined via the `instructions` parameter of the [`Agent` constructor][pydantic_ai.Agent.__init__].
 2. **Dynamic instructions**: These rely on context that is only available at runtime and should be defined using functions decorated with [`@agent.instructions`][pydantic_ai.Agent.instructions]. Unlike dynamic system prompts, which may be reused when `message_history` is present, dynamic instructions are always reevaluated.
+3. **Runtime instructions*: These are additional instructions for a specific run that can be passed to one of the [run methods](#running-agents) using the `instructions` argument.
 
-Both static and dynamic instructions can be added to a single agent, and they are appended in the order they are defined at runtime.
+All three types of instructions can be added to a single agent, and they are appended in the order they are defined at runtime.
 
-Here's an example using both types of instructions:
+Here's an example using a static instruction as well as dynamic instructions:
 
 ```python {title="instructions.py"}
 from datetime import date
diff --git a/pydantic_ai_slim/pydantic_ai/agent/__init__.py b/pydantic_ai_slim/pydantic_ai/agent/__init__.py
index 6515bb7afe..fd0f59ff38 100644
--- a/pydantic_ai_slim/pydantic_ai/agent/__init__.py
+++ b/pydantic_ai_slim/pydantic_ai/agent/__init__.py
@@ -238,7 +238,7 @@ def __init__(
             output_type: The type of the output data, used to validate the data returned by the model,
                 defaults to `str`.
             instructions: Instructions to use for this agent, you can also register instructions via a function with
-                [`instructions`][pydantic_ai.Agent.instructions].
+                [`instructions`][pydantic_ai.Agent.instructions] or pass additional, temporary, instructions when executing a run.
             system_prompt: Static system prompts to use for this agent, you can also register system
                 prompts via a function with [`system_prompt`][pydantic_ai.Agent.system_prompt].
             deps_type: The type used for dependency injection, this parameter exists solely to allow you to fully
@@ -418,6 +418,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -436,6 +437,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -454,6 +456,7 @@ async def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -527,6 +530,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -580,7 +584,7 @@ async def main():
         model_settings = merge_model_settings(merged_settings, model_settings)
         usage_limits = usage_limits or _usage.UsageLimits()
 
-        instructions_literal, instructions_functions = self._get_instructions()
+        instructions_literal, instructions_functions = self._get_instructions(additional_instructions=instructions)
 
         async def get_instructions(run_context: RunContext[AgentDepsT]) -> str | None:
             parts = [
@@ -1330,9 +1334,15 @@ def _normalize_instructions(
 
     def _get_instructions(
         self,
+        additional_instructions: Instructions[AgentDepsT] = None,
     ) -> tuple[str | None, list[_system_prompt.SystemPromptRunner[AgentDepsT]]]:
         override_instructions = self._override_instructions.get()
-        instructions = override_instructions.value if override_instructions else self._instructions
+        if override_instructions:
+            instructions = override_instructions.value
+        else:
+            instructions = self._instructions.copy()
+            if additional_instructions is not None:
+                instructions.extend(self._normalize_instructions(additional_instructions))
 
         literal_parts: list[str] = []
         functions: list[_system_prompt.SystemPromptRunner[AgentDepsT]] = []
diff --git a/pydantic_ai_slim/pydantic_ai/agent/abstract.py b/pydantic_ai_slim/pydantic_ai/agent/abstract.py
index 302fdc83dd..fa5846a31d 100644
--- a/pydantic_ai_slim/pydantic_ai/agent/abstract.py
+++ b/pydantic_ai_slim/pydantic_ai/agent/abstract.py
@@ -131,6 +131,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -150,6 +151,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -168,6 +170,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -201,6 +204,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -224,6 +228,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -250,6 +255,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -269,6 +275,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -287,6 +294,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -319,6 +327,7 @@ def run_sync(
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -341,6 +350,7 @@ def run_sync(
                 message_history=message_history,
                 deferred_tool_results=deferred_tool_results,
                 model=model,
+                instructions=instructions,
                 deps=deps,
                 model_settings=model_settings,
                 usage_limits=usage_limits,
@@ -361,6 +371,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -380,6 +391,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -399,6 +411,7 @@ async def run_stream(  # noqa C901
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -439,6 +452,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -468,6 +482,7 @@ async def main():
             deferred_tool_results=deferred_tool_results,
             model=model,
             deps=deps,
+            instructions=instructions,
             model_settings=model_settings,
             usage_limits=usage_limits,
             usage=usage,
@@ -716,6 +731,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -734,6 +750,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -751,6 +768,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -800,6 +818,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -824,6 +843,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -840,6 +860,7 @@ async def _run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -865,6 +886,7 @@ async def run_agent() -> AgentRunResult[Any]:
                     message_history=message_history,
                     deferred_tool_results=deferred_tool_results,
                     model=model,
+                    instructions=instructions,
                     deps=deps,
                     model_settings=model_settings,
                     usage_limits=usage_limits,
@@ -893,6 +915,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -911,6 +934,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -930,6 +954,7 @@ async def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -1003,6 +1028,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
diff --git a/pydantic_ai_slim/pydantic_ai/agent/wrapper.py b/pydantic_ai_slim/pydantic_ai/agent/wrapper.py
index a770244919..fcf7826f13 100644
--- a/pydantic_ai_slim/pydantic_ai/agent/wrapper.py
+++ b/pydantic_ai_slim/pydantic_ai/agent/wrapper.py
@@ -76,6 +76,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -94,6 +95,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -112,6 +114,7 @@ async def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -185,6 +188,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -202,6 +206,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
diff --git a/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py b/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py
index 2f4a19752c..42aec0bd83 100644
--- a/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py
+++ b/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py
@@ -116,6 +116,7 @@ async def wrapped_run_workflow(
             message_history: Sequence[_messages.ModelMessage] | None = None,
             deferred_tool_results: DeferredToolResults | None = None,
             model: models.Model | models.KnownModelName | str | None = None,
+            instructions: Instructions[AgentDepsT] = None,
             deps: AgentDepsT,
             model_settings: ModelSettings | None = None,
             usage_limits: _usage.UsageLimits | None = None,
@@ -133,6 +134,7 @@ async def wrapped_run_workflow(
                     message_history=message_history,
                     deferred_tool_results=deferred_tool_results,
                     model=model,
+                    instructions=instructions,
                     deps=deps,
                     model_settings=model_settings,
                     usage_limits=usage_limits,
@@ -157,6 +159,7 @@ def wrapped_run_sync_workflow(
             model: models.Model | models.KnownModelName | str | None = None,
             deps: AgentDepsT,
             model_settings: ModelSettings | None = None,
+            instructions: Instructions[AgentDepsT] = None,
             usage_limits: _usage.UsageLimits | None = None,
             usage: _usage.RunUsage | None = None,
             infer_name: bool = True,
@@ -172,6 +175,7 @@ def wrapped_run_sync_workflow(
                     message_history=message_history,
                     deferred_tool_results=deferred_tool_results,
                     model=model,
+                    instructions=instructions,
                     deps=deps,
                     model_settings=model_settings,
                     usage_limits=usage_limits,
@@ -245,6 +249,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -264,6 +269,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -282,6 +288,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -316,6 +323,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -334,6 +342,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -354,6 +363,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -373,6 +383,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -391,6 +402,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -424,6 +436,7 @@ def run_sync(
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -442,6 +455,7 @@ def run_sync(
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -462,6 +476,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -482,6 +497,7 @@ def run_stream(
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
+        instructions: Instructions[AgentDepsT] = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
         usage: _usage.RunUsage | None = None,
@@ -500,6 +516,7 @@ async def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -531,6 +548,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -555,6 +573,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -576,6 +595,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -594,6 +614,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -611,6 +632,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -660,6 +682,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -686,6 +709,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -705,6 +729,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -724,6 +749,7 @@ async def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -798,6 +824,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -821,6 +848,7 @@ async def main():
                 message_history=message_history,
                 deferred_tool_results=deferred_tool_results,
                 model=model,
+                instructions=instructions,
                 deps=deps,
                 model_settings=model_settings,
                 usage_limits=usage_limits,
diff --git a/pydantic_ai_slim/pydantic_ai/durable_exec/prefect/_agent.py b/pydantic_ai_slim/pydantic_ai/durable_exec/prefect/_agent.py
index 6d622e56f4..0867a60e36 100644
--- a/pydantic_ai_slim/pydantic_ai/durable_exec/prefect/_agent.py
+++ b/pydantic_ai_slim/pydantic_ai/durable_exec/prefect/_agent.py
@@ -180,6 +180,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -199,6 +200,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -217,6 +219,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -251,6 +254,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -276,6 +280,7 @@ async def wrapped_run_flow() -> AgentRunResult[Any]:
                         message_history=message_history,
                         deferred_tool_results=deferred_tool_results,
                         model=model,
+                        instructions=instructions,
                         deps=deps,
                         model_settings=model_settings,
                         usage_limits=usage_limits,
@@ -299,6 +304,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -318,6 +324,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -336,6 +343,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -369,6 +377,7 @@ def run_sync(
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -396,6 +405,7 @@ def wrapped_run_sync_flow() -> AgentRunResult[Any]:
                             message_history=message_history,
                             deferred_tool_results=deferred_tool_results,
                             model=model,
+                            instructions=instructions,
                             deps=deps,
                             model_settings=model_settings,
                             usage_limits=usage_limits,
@@ -420,6 +430,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -439,6 +450,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -458,6 +470,7 @@ async def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -489,6 +502,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -513,6 +527,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -534,6 +549,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -552,6 +568,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -569,6 +586,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -618,6 +636,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -642,6 +661,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -660,6 +680,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -678,6 +699,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -696,6 +718,7 @@ async def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -770,6 +793,7 @@ async def main():
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
             deps: Optional dependencies to use for this run.
+            instructions: Optional additional instructions to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
             usage: Optional usage to start with, useful for resuming a conversation or agents used in tools.
@@ -792,6 +816,7 @@ async def main():
                 message_history=message_history,
                 deferred_tool_results=deferred_tool_results,
                 model=model,
+                instructions=instructions,
                 deps=deps,
                 model_settings=model_settings,
                 usage_limits=usage_limits,
diff --git a/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py b/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py
index 958a43d1bb..b6be1e7b9d 100644
--- a/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py
+++ b/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py
@@ -263,6 +263,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -282,6 +283,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -300,6 +302,7 @@ async def run(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -334,6 +337,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -358,6 +362,7 @@ async def main():
                 message_history=message_history,
                 deferred_tool_results=deferred_tool_results,
                 model=model,
+                instructions=instructions,
                 deps=deps,
                 model_settings=model_settings,
                 usage_limits=usage_limits,
@@ -378,6 +383,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -397,6 +403,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -415,6 +422,7 @@ def run_sync(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -448,6 +456,7 @@ def run_sync(
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -471,6 +480,7 @@ def run_sync(
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -491,6 +501,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -510,6 +521,7 @@ def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -529,6 +541,7 @@ async def run_stream(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -560,6 +573,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -584,6 +598,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -605,6 +620,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -623,6 +639,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -640,6 +657,7 @@ def run_stream_events(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -689,6 +707,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -713,6 +732,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
@@ -731,6 +751,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -750,6 +771,7 @@ def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -769,6 +791,7 @@ async def iter(
         message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
+        instructions: Instructions[AgentDepsT] = None,
         deps: AgentDepsT = None,
         model_settings: ModelSettings | None = None,
         usage_limits: _usage.UsageLimits | None = None,
@@ -843,6 +866,7 @@ async def main():
             message_history: History of the conversation so far.
             deferred_tool_results: Optional results for deferred tool calls in the message history.
             model: Optional model to use for this run, required if `model` was not set when creating the agent.
+            instructions: Optional additional instructions to use for this run.
             deps: Optional dependencies to use for this run.
             model_settings: Optional settings to use for this model's request.
             usage_limits: Optional limits on model request count or token usage.
@@ -876,6 +900,7 @@ async def main():
             message_history=message_history,
             deferred_tool_results=deferred_tool_results,
             model=model,
+            instructions=instructions,
             deps=deps,
             model_settings=model_settings,
             usage_limits=usage_limits,
diff --git a/tests/test_agent.py b/tests/test_agent.py
index 2b8d53007c..a05359b145 100644
--- a/tests/test_agent.py
+++ b/tests/test_agent.py
@@ -3897,6 +3897,30 @@ def empty_instructions() -> str:
     )
 
 
+def test_instructions_during_run():
+    agent = Agent('test', instructions='You are a helpful assistant.')
+    result = agent.run_sync('Hello', instructions='Your task is to greet people.')
+    assert result.all_messages()[0] == snapshot(
+        ModelRequest(
+            parts=[UserPromptPart(content='Hello', timestamp=IsDatetime())],
+            instructions="""\
+You are a helpful assistant.
+Your task is to greet people.\
+""",
+        )
+    )
+
+    result2 = agent.run_sync('Hello again!')
+    assert result2.all_messages()[0] == snapshot(
+        ModelRequest(
+            parts=[UserPromptPart(content='Hello again!', timestamp=IsDatetime())],
+            instructions="""\
+You are a helpful assistant.\
+""",
+        )
+    )
+
+
 def test_multi_agent_instructions_with_structured_output():
     """Test that Agent2 uses its own instructions when called with Agent1's history.