Update changelog/upgrade guide for V1 (#2810)

Author: DouweM

docs/changelog.md

@@ -1,36 +1,44 @@
 # Upgrade Guide
 
-Pydantic AI is still pre-version 1, so breaking changes will occur, however:
-
-- We try to minimize them as much as possible.
-- We use minor version bumps to signify breaking changes.
-- Wherever possible we deprecate old features so code continues to work with deprecation warnings when changing the public API.
-- We intend to release V1 in summer 2025, and then follow strict semantic versioning, e.g. no intentional breaking changes except in minor or patch versions.
+In September 2025, Pydantic AI reached V1, which means we're committed to API stability: we will not introduce changes that break your code until V2 (if we do, you can shout at us as it's definitely a mistake).
+Once we release V2, in April 2026 at the earliest, we'll continue to provide security fixes for V1 for another 6 months minimum, so you have time to upgrade your applications.
 
 ## Breaking Changes
 
-!!! note
-    Here's a filtered list of the breaking changes for each version to help you upgrade Pydantic AI.
+Here's a filtered list of the breaking changes for each version to help you upgrade Pydantic AI.
+
+### v1.0.0 (2025-09-04)
+
+- See [#2725](https://github.com/pydantic/pydantic-ai/pull/2725) - Drop support for Python 3.9
+- See [#2738](https://github.com/pydantic/pydantic-ai/pull/2738) - Make many dataclasses require keyword arguments
+- See [#2715](https://github.com/pydantic/pydantic-ai/pull/2715) - Remove `cases` and `averages` attributes from `pydantic_evals` spans
+- See [#2798](https://github.com/pydantic/pydantic-ai/pull/2798) - Change `ModelRequest.parts` and `ModelResponse.parts` types from `list` to `Sequence`
+- See [#2726](https://github.com/pydantic/pydantic-ai/pull/2726) - Default `InstrumentationSettings` version to 2
+- See [#2717](https://github.com/pydantic/pydantic-ai/pull/2717) - Remove errors when passing `AsyncRetrying` or `Retrying` object to `AsyncTenacityTransport` or `TenacityTransport` instead of `RetryConfig`
 
-### v0.8.0 (2025-08-26)
+### v0.x.x
+
+Before V1, minor versions were used to introduce breaking changes:
+
+**v0.8.0 (2025-08-26)**
 
 See [#2689](https://github.com/pydantic/pydantic-ai/pull/2689) - `AgentStreamEvent` was expanded to be a union of `ModelResponseStreamEvent` and `HandleResponseEvent`, simplifying the `event_stream_handler` function signature. Existing code accepting `AgentStreamEvent | HandleResponseEvent` will continue to work.
 
-### v0.7.6 (2025-08-26)
+**v0.7.6 (2025-08-26)**
 
 The following breaking change was inadvertently released in a patch version rather than a minor version:
 
 See [#2670](https://github.com/pydantic/pydantic-ai/pull/2670) - `TenacityTransport` and `AsyncTenacityTransport` now require the use of `pydantic_ai.retries.RetryConfig` (which is just a `TypedDict` containing the kwargs to `tenacity.retry`) instead of `tenacity.Retrying` or `tenacity.AsyncRetrying`.
 
-### v0.7.0 (2025-08-12)
+**v0.7.0 (2025-08-12)**
 
 See [#2458](https://github.com/pydantic/pydantic-ai/pull/2458) - `pydantic_ai.models.StreamedResponse` now yields a `FinalResultEvent` along with the existing `PartStartEvent` and `PartDeltaEvent`. If you're using `pydantic_ai.direct.model_request_stream` or `pydantic_ai.direct.model_request_stream_sync`, you may need to update your code to account for this.
 
 See [#2458](https://github.com/pydantic/pydantic-ai/pull/2458) - `pydantic_ai.models.Model.request_stream` now receives a `run_context` argument. If you've implemented a custom `Model` subclass, you will need to account for this.
 
 See [#2458](https://github.com/pydantic/pydantic-ai/pull/2458) - `pydantic_ai.models.StreamedResponse` now requires a `model_request_parameters` field and constructor argument. If you've implemented a custom `Model` subclass and implemented `request_stream`, you will need to account for this.
 
-### v0.6.0 (2025-08-06)
+**v0.6.0 (2025-08-06)**
 
 This release was meant to clean some old deprecated code, so we can get a step closer to V1.
 
@@ -50,19 +58,19 @@ Import it via `from pydantic_ai import format_as_xml` instead.
 
 See [#2451](https://github.com/pydantic/pydantic-ai/pull/2451) - Removed deprecated `Agent.result_validator` method, `Agent.last_run_messages` property, `AgentRunResult.data` property, and `result_tool_return_content` parameters from result classes.
 
-### v0.5.0 (2025-08-04)
+**v0.5.0 (2025-08-04)**
 
 See [#2388](https://github.com/pydantic/pydantic-ai/pull/2388) - The `source` field of an `EvaluationResult` is now of type `EvaluatorSpec` rather than the actual source `Evaluator` instance, to help with serialization/deserialization.
 
 See [#2163](https://github.com/pydantic/pydantic-ai/pull/2163) - The `EvaluationReport.print` and `EvaluationReport.console_table` methods now require most arguments be passed by keyword.
 
-### v0.4.0 (2025-07-08)
+**v0.4.0 (2025-07-08)**
 
 See [#1799](https://github.com/pydantic/pydantic-ai/pull/1799) - Pydantic Evals `EvaluationReport` and `ReportCase` are now generic dataclasses instead of Pydantic models. If you were serializing them using `model_dump()`, you will now need to use the `EvaluationReportAdapter` and `ReportCaseAdapter` type adapters instead.
 
 See [#1507](https://github.com/pydantic/pydantic-ai/pull/1507) - The `ToolDefinition` `description` argument is now optional and the order of positional arguments has changed from `name, description, parameters_json_schema, ...` to `name, parameters_json_schema, description, ...` to account for this.
 
-### v0.3.0 (2025-06-18)
+**v0.3.0 (2025-06-18)**
 
 See [#1142](https://github.com/pydantic/pydantic-ai/pull/1142) — Adds support for thinking parts.
 
@@ -71,21 +79,19 @@ Pydantic AI `ThinkingPart`s. Also, as part of this release, we made the choice t
 `ThinkingPart`s to the provider - the idea is to save costs on behalf of the user. In the future, we
 intend to add a setting to customize this behavior.
 
-### v0.2.0 (2025-05-12)
+**v0.2.0 (2025-05-12)**
 
 See [#1647](https://github.com/pydantic/pydantic-ai/pull/1647) — usage makes sense as part of `ModelResponse`, and could be really useful in "messages" (really a sequence of requests and response). In this PR:
 
 - Adds `usage` to `ModelResponse` (field has a default factory of `Usage()` so it'll work to load data that doesn't have usage)
 - changes the return type of `Model.request` to just `ModelResponse` instead of `tuple[ModelResponse, Usage]`
 
-### v0.1.0 (2025-04-15)
+**v0.1.0 (2025-04-15)**
 
 See [#1248](https://github.com/pydantic/pydantic-ai/pull/1248) — the attribute/parameter name `result` was renamed to `output` in many places. Hopefully all changes keep a deprecated attribute or parameter with the old name, so you should get many deprecation warnings.
 
 See [#1484](https://github.com/pydantic/pydantic-ai/pull/1484) — `format_as_xml` was moved and made available to import from the package root, e.g. `from pydantic_ai import format_as_xml`.
 
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-
 ## Full Changelog
 
 <div id="display-changelog">