diff --git a/.changeset/ready-items-shout.md b/.changeset/ready-items-shout.md
new file mode 100644
index 000000000..e96b78718
--- /dev/null
+++ b/.changeset/ready-items-shout.md
@@ -0,0 +1,9 @@
+---
+'@openfn/engine-multi': minor
+'@openfn/ws-worker': minor
+'@openfn/runtime': minor
+---
+
+Measure the size of state objects at the end of each step, and throw if they exceed a limit
+
+In the Worker, this limit is set to 25% of the available runtime memory.
diff --git a/packages/engine-multi/src/api/execute.ts b/packages/engine-multi/src/api/execute.ts
index fabdf4b11..9e6cd0ea4 100644
--- a/packages/engine-multi/src/api/execute.ts
+++ b/packages/engine-multi/src/api/execute.ts
@@ -46,8 +46,17 @@ const execute = async (context: ExecutionContext) => {
       repoDir: options.repoDir,
       profile: context.options.profile,
       profilePollInteval: context.options.profilePollInterval,
+      // work out the max size of the state object at the end of each step
+      // This must be fairly high to prevent crashes
+      stateLimitMb:
+        options.stateLimitMb ??
+        Math.max((options.memoryLimitMb ?? 1000) * 0.25),
     } as RunOptions;
 
+    logger.debug(
+      `${state.plan.id} setting runtime state limit to ${runOptions.stateLimitMb}mb`
+    );
+
     // Construct the payload limits object
     const payloadLimits: PayloadLimits = {};
     if (options.payloadLimitMb !== undefined) {
diff --git a/packages/engine-multi/src/engine.ts b/packages/engine-multi/src/engine.ts
index adf2bb88b..630e334ab 100644
--- a/packages/engine-multi/src/engine.ts
+++ b/packages/engine-multi/src/engine.ts
@@ -167,6 +167,7 @@ const createEngine = async (
       callWorker,
       options: {
         ...options,
+        stateLimitMb: opts.stateLimitMb,
         sanitize: opts.sanitize,
         resolvers: opts.resolvers,
         runTimeoutMs: opts.runTimeoutMs ?? defaultTimeout,
diff --git a/packages/engine-multi/src/types.ts b/packages/engine-multi/src/types.ts
index e42255b1b..ae2a44b7a 100644
--- a/packages/engine-multi/src/types.ts
+++ b/packages/engine-multi/src/types.ts
@@ -45,6 +45,7 @@ export type ExecutionContextConstructor = {
 };
 
 export type ExecuteOptions = {
+  stateLimitMb?: number;
   payloadLimitMb?: number;
   logPayloadLimitMb?: number;
   memoryLimitMb?: number;
@@ -72,7 +73,7 @@ export interface RuntimeEngine {
   execute(
     plan: ExecutionPlan,
     input: State,
-    options?: Partial<EngineOptions>
+    options?: ExecuteOptions
   ): Pick<EventEmitter, 'on' | 'off' | 'once'>;
 
   destroy(instant?: boolean): Promise<void>;
diff --git a/packages/engine-multi/src/worker/thread/run.ts b/packages/engine-multi/src/worker/thread/run.ts
index 8d54d9a72..a388faf0f 100644
--- a/packages/engine-multi/src/worker/thread/run.ts
+++ b/packages/engine-multi/src/worker/thread/run.ts
@@ -20,6 +20,7 @@ export type RunOptions = {
   jobLogLevel?: LogLevel;
   profile?: boolean;
   profilePollInterval?: number;
+  stateLimitMb?: number;
 };
 
 const eventMap = {
@@ -39,6 +40,7 @@ register({
       jobLogLevel,
       profile,
       profilePollInterval,
+      stateLimitMb,
     } = runOptions;
     const { logger, jobLogger, adaptorLogger } = createLoggers(
       plan.id!,
@@ -54,9 +56,8 @@ register({
     console = adaptorLogger;
 
     // Leave console.debug for local debugging
-    // This goes to stdout but not the adapator logger
+    // This goes to stdout but not the adaptor logger
     console.debug = debug;
-
     // TODO I would like to pull these options out of here
     const options = {
       // disable the runtime's own timeout
@@ -72,6 +73,7 @@ register({
       profile,
       profilePollInterval,
       statePropsToRemove,
+      stateLimitMb,
       callbacks: {
         // TODO: this won't actually work across the worker boundary
         // For now I am preloading credentials
diff --git a/packages/engine-multi/test/errors.test.ts b/packages/engine-multi/test/errors.test.ts
index a206b37d2..15781753f 100644
--- a/packages/engine-multi/test/errors.test.ts
+++ b/packages/engine-multi/test/errors.test.ts
@@ -165,6 +165,35 @@ test.serial.skip('vm oom error', (t) => {
   });
 });
 
+test.serial('state object too big', async (t) => {
+  return new Promise((done) => {
+    const plan = {
+      id: 'x',
+      workflow: {
+        steps: [
+          {
+            expression: `export default [(s) => {
+              s.data = new Array(1024 * 1024).fill("x").join("");
+              return s;
+            }]`,
+          },
+        ],
+      },
+    };
+
+    const options = {
+      stateLimitMb: 0.1,
+    };
+
+    engine.execute(plan, {}, options).on(WORKFLOW_ERROR, (evt) => {
+      t.is(evt.type, 'StateTooLargeError');
+      t.is(evt.severity, 'kill');
+      t.is(evt.message, 'State exceeds the limit of 0.1mb');
+      done();
+    });
+  });
+});
+
 test.serial('execution error from async code', (t) => {
   return new Promise((done) => {
     const plan = {
diff --git a/packages/runtime/package.json b/packages/runtime/package.json
index 3bcad74bc..1e87fa818 100644
--- a/packages/runtime/package.json
+++ b/packages/runtime/package.json
@@ -48,6 +48,7 @@
   "dependencies": {
     "@openfn/logger": "workspace:*",
     "fast-safe-stringify": "^2.1.1",
+    "json-stream-stringify": "^3.1.6",
     "semver": "^7.7.2",
     "source-map": "^0.7.6"
   }
diff --git a/packages/runtime/src/errors.ts b/packages/runtime/src/errors.ts
index c31ec5a57..2279df992 100644
--- a/packages/runtime/src/errors.ts
+++ b/packages/runtime/src/errors.ts
@@ -91,6 +91,15 @@ export const extractStackTrace = (e: Error) => {
   }
 };
 
+export class StateTooLargeError extends Error {
+  name = 'StateTooLargeError';
+  severity = 'kill';
+  constructor(limit_mb: number) {
+    super();
+    this.message = `State exceeds the limit of ${limit_mb}mb`;
+  }
+}
+
 // Abstract error supertype
 export class RTError extends Error {
   source = 'runtime';
diff --git a/packages/runtime/src/execute/step.ts b/packages/runtime/src/execute/step.ts
index 1e72168ea..e30912270 100644
--- a/packages/runtime/src/execute/step.ts
+++ b/packages/runtime/src/execute/step.ts
@@ -20,6 +20,7 @@ import {
 import { isNullState } from '../util/null-state';
 import sourcemapErrors from '../util/sourcemap-errors';
 import createProfiler from '../util/profile-memory';
+import ensureStateSize from '../util/ensure-state-size';
 
 const loadCredentials = async (
   job: Job,
@@ -79,13 +80,21 @@ const calculateNext = (job: CompiledStep, result: any, logger: Logger) => {
 
 // TODO this is suboptimal and may be slow on large objects
 // (especially as the result get stringified again downstream)
-const prepareFinalState = (
+const prepareFinalState = async (
   state: any,
   logger: Logger,
-  statePropsToRemove?: string[]
+  statePropsToRemove?: string[],
+  stateLimit_mb?: number
 ) => {
   if (isNullState(state)) return undefined;
   if (state) {
+    try {
+      await ensureStateSize(state, stateLimit_mb);
+    } catch (e) {
+      logger.error('Critical error processing state:');
+      throw e;
+    }
+
     if (!statePropsToRemove) {
       // As a strict default, remove the configuration key
       // tbh this should happen higher up in the stack but it causes havoc in unit testing
@@ -190,7 +199,12 @@ const executeStep = async (
         const duration = logger.timer(timerId);
         logger.error(`${jobName} aborted with error (${duration})`);
 
-        state = prepareFinalState(state, logger, ctx.opts.statePropsToRemove);
+        state = await prepareFinalState(
+          state,
+          logger,
+          ctx.opts.statePropsToRemove,
+          ctx.opts.stateLimitMb
+        );
         // Whatever the final state was, save that as the initial state to the next thing
         result = state;
 
@@ -219,7 +233,12 @@ const executeStep = async (
     if (!didError) {
       const humanDuration = logger.timer(timerId);
       logger.success(`${jobName} completed in ${humanDuration}`);
-      result = prepareFinalState(result, logger, ctx.opts.statePropsToRemove);
+      result = await prepareFinalState(
+        result,
+        logger,
+        ctx.opts.statePropsToRemove,
+        ctx.opts.stateLimitMb
+      );
 
       // Take a memory snapshot
       // IMPORTANT: this runs _after_ the state object has been serialized
diff --git a/packages/runtime/src/runtime.ts b/packages/runtime/src/runtime.ts
index 11b60f6c0..ba47d0327 100644
--- a/packages/runtime/src/runtime.ts
+++ b/packages/runtime/src/runtime.ts
@@ -38,6 +38,8 @@ export type Options = {
 
   /** Optional name for the expression (if passed a string) */
   defaultStepId?: string;
+
+  stateLimitMb?: number;
 };
 
 type RawOptions = Omit<Options, 'linker'> & {
diff --git a/packages/runtime/src/util/clone.ts b/packages/runtime/src/util/clone.ts
index 0920f7106..e1f3f9add 100644
--- a/packages/runtime/src/util/clone.ts
+++ b/packages/runtime/src/util/clone.ts
@@ -1,6 +1,4 @@
 import type { State } from '@openfn/lexicon';
 import stringify from 'fast-safe-stringify';
 
-// TODO I'm in the market for the best solution here - immer? deep-clone?
-// What should we do if functions are in the state?
 export default (state: State) => JSON.parse(stringify(state));
diff --git a/packages/runtime/src/util/ensure-state-size.ts b/packages/runtime/src/util/ensure-state-size.ts
new file mode 100644
index 000000000..f884d1d44
--- /dev/null
+++ b/packages/runtime/src/util/ensure-state-size.ts
@@ -0,0 +1,34 @@
+import { JsonStreamStringify } from 'json-stream-stringify';
+import { StateTooLargeError } from '../errors';
+
+const replacer = (_key: string, value: any) => {
+  // Ignore non serializable keys
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    value?.constructor?.name === 'Promise'
+  ) {
+    return undefined;
+  }
+
+  return value;
+};
+
+// throws if state exceeds a particular size limit
+export default async (value: any, limit_mb: number = 500) => {
+  if (value && !isNaN(limit_mb) && limit_mb > 0) {
+    const limitBytes = limit_mb * 1024 * 1024;
+    let size_bytes = 0;
+    const stream = new JsonStreamStringify(value, replacer, 0, true);
+    for await (const chunk of stream) {
+      // Each chunk is a string token from the JSON output
+      size_bytes += Buffer.byteLength(chunk, 'utf8');
+
+      if (size_bytes > limitBytes) {
+        stream.destroy();
+        throw new StateTooLargeError(limit_mb);
+      }
+    }
+    stream.destroy();
+  }
+};
diff --git a/packages/runtime/test/runtime.test.ts b/packages/runtime/test/runtime.test.ts
index 209fdf865..adcf52bed 100644
--- a/packages/runtime/test/runtime.test.ts
+++ b/packages/runtime/test/runtime.test.ts
@@ -899,3 +899,40 @@ test('accept a whitelist as a string', async (t) => {
     t.is(error.message, 'module blacklisted: blah');
   }
 });
+
+test('do not enforce state size limit if state is small enough', async (t) => {
+  const plan: ExecutionPlan = {
+    workflow: {
+      steps: [
+        {
+          expression:
+            'export default [(s) => { s.data.large = new Array(1024).fill("z").join(""); return s; }]',
+        },
+      ],
+    },
+  };
+
+  await run(plan, {}, {});
+  t.pass('did not fail');
+});
+
+test('enforce state size limit from runtime option', async (t) => {
+  const plan: ExecutionPlan = {
+    workflow: {
+      steps: [
+        {
+          expression:
+            'export default [(s) => { s.data.large = new Array(1024).fill("z").join(""); return s; }]',
+        },
+      ],
+    },
+  };
+
+  try {
+    await run(plan, {}, { stateLimitMb: 1 / 1024 });
+    t.fail('Should have thrown StateTooLargeError');
+  } catch (error: any) {
+    t.is(error.name, 'StateTooLargeError');
+    t.regex(error.message, /State exceeds the limit/);
+  }
+});
diff --git a/packages/runtime/test/util/ensure-state-size.test.ts b/packages/runtime/test/util/ensure-state-size.test.ts
new file mode 100644
index 000000000..dfb5616e3
--- /dev/null
+++ b/packages/runtime/test/util/ensure-state-size.test.ts
@@ -0,0 +1,108 @@
+import test from 'ava';
+import ensureStateSize from '../../src/util/ensure-state-size';
+import { StateTooLargeError } from '../../src/errors';
+
+test('do not throw for limit 0kb', async (t) => {
+  const state = { data: new Array(1024).fill('z').join('') };
+  await t.notThrowsAsync(() => ensureStateSize(state, 0));
+});
+
+test('throw for limit 1kb, payload 1kb', async (t) => {
+  const state = { data: new Array(1024).fill('z').join('') };
+  await t.throwsAsync(() => ensureStateSize(state, 1 / 1024), {
+    instanceOf: StateTooLargeError,
+    message: 'State exceeds the limit of 0.0009765625mb',
+  });
+});
+
+test('ok for limit 2kb, payload 1kb', async (t) => {
+  const state = { data: new Array(1024).fill('z').join('') };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('allow circular references', async (t) => {
+  const state: any = { data: 'test' };
+  state.self = state;
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('allow circular references 2', async (t) => {
+  const arr = [{ id: 1 }, { id: 2 }, { id: 3 }];
+  const state: any = { data: arr, arr };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle promise in state', async (t) => {
+  const state = {
+    data: 'test',
+    promise: new Promise((r) => r),
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle function in state', async (t) => {
+  const state = {
+    data: 'test',
+    fn: () => 'hello',
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle undefined in state', async (t) => {
+  const state = {
+    data: 'test',
+    undef: undefined,
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle symbol in state', async (t) => {
+  const state = {
+    data: 'test',
+    sym: Symbol('test'),
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle BigInt in state', async (t) => {
+  const state = {
+    data: 'test',
+    big: BigInt(123456789),
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle Date in state', async (t) => {
+  const state = {
+    data: 'test',
+    date: new Date('2024-01-01'),
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle RegExp in state', async (t) => {
+  const state = {
+    data: 'test',
+    regex: /test/gi,
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle Map in state', async (t) => {
+  const map = new Map();
+  map.set('key', 'value');
+  const state = {
+    data: 'test',
+    map: map,
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
+
+test('handle Set in state', async (t) => {
+  const set = new Set([1, 2, 3]);
+  const state = {
+    data: 'test',
+    set: set,
+  };
+  await t.notThrowsAsync(() => ensureStateSize(state, 2 / 1024));
+});
diff --git a/packages/ws-worker/src/mock/runtime-engine.ts b/packages/ws-worker/src/mock/runtime-engine.ts
index 282168b7e..2d76b0b74 100644
--- a/packages/ws-worker/src/mock/runtime-engine.ts
+++ b/packages/ws-worker/src/mock/runtime-engine.ts
@@ -74,7 +74,7 @@ async function createMock() {
     for (const step of steps) {
       const job = step as Job;
       if (typeof job.configuration === 'string') {
-        // Call the crendtial callback, but don't do anything with it
+        // Call the credential callback, but don't do anything with it
         job.configuration = await options.resolvers?.credential?.(
           job.configuration
         );
diff --git a/packages/ws-worker/src/server.ts b/packages/ws-worker/src/server.ts
index 6e8cd7c39..88c09bdb4 100644
--- a/packages/ws-worker/src/server.ts
+++ b/packages/ws-worker/src/server.ts
@@ -312,6 +312,7 @@ function createServer(engine: RuntimeEngine, options: ServerOptions = {}) {
         if (!('logPayloadLimitMb' in options)) {
           options.logPayloadLimitMb = app.options.logPayloadLimitMb;
         }
+
         options.timeoutRetryCount = app.options.timeoutRetryCount;
         options.timeoutRetryDelay =
           app.options.timeoutRetryDelayMs ?? app.options.socketTimeoutSeconds;
diff --git a/packages/ws-worker/test/lightning.test.ts b/packages/ws-worker/test/lightning.test.ts
index 3f2deeb4a..a16f2b5fa 100644
--- a/packages/ws-worker/test/lightning.test.ts
+++ b/packages/ws-worker/test/lightning.test.ts
@@ -181,14 +181,14 @@ test.serial(`should reset backoff after claim`, (t) => {
     });
 
     lng.onSocketEvent(e.RUN_COMPLETE, run.id, () => {
-      // set this articially high - if there are no more claims, the test will fail
+      // set this artificially high - if there are no more claims, the test will fail
       lastClaimDiff = 10000;
 
       // When the run is finished, the claims should resume
       // but with a smaller backoff
       setTimeout(() => {
         t.log('Backoff after run:', lastClaimDiff);
-        t.true(lastClaimDiff < 5);
+        t.true(lastClaimDiff < 10);
         done();
       }, 10);
     });
diff --git a/packages/ws-worker/test/mock/runtime-engine.test.ts b/packages/ws-worker/test/mock/runtime-engine.test.ts
index 28842769e..a876baf07 100644
--- a/packages/ws-worker/test/mock/runtime-engine.test.ts
+++ b/packages/ws-worker/test/mock/runtime-engine.test.ts
@@ -1,15 +1,16 @@
 import test from 'ava';
 import type { ExecutionPlan } from '@openfn/lexicon';
 
+import create from '../../src/mock/runtime-engine';
+import { waitForEvent, clone, createPlan } from '../util';
+
 import type {
   JobCompletePayload,
   JobStartPayload,
   WorkflowCompletePayload,
   WorkflowStartPayload,
 } from '@openfn/engine-multi';
-import create from '../../src/mock/runtime-engine';
-import { waitForEvent, clone, createPlan } from '../util';
-import { WorkflowErrorPayload } from '@openfn/engine-multi';
+import type { WorkflowErrorPayload } from '@openfn/engine-multi';
 
 const sampleWorkflow = {
   id: 'w1',
@@ -117,21 +118,30 @@ test.serial('wait function', async (t) => {
 test.serial(
   'resolve credential before job-start if credential is a string',
   async (t) => {
-    const wf = clone(sampleWorkflow);
-    wf.id = t.title;
-    wf.workflow.steps[0].configuration = 'x';
-
-    let didCallCredentials;
-    const credential = async () => {
-      didCallCredentials = true;
-      return {};
-    };
-
-    // @ts-ignore
-    engine.execute(wf, {}, { resolvers: { credential } });
-
-    await waitForEvent<JobStartPayload>(engine, 'job-start');
-    t.true(didCallCredentials);
+    t.plan(1);
+    return new Promise((resolve) => {
+      const wf = clone(sampleWorkflow);
+      wf.id = t.title;
+      wf.workflow.steps[0].configuration = 'x';
+
+      let didCallCredentials = false;
+      const credential = async () => {
+        didCallCredentials = true;
+        return {};
+      };
+
+      engine.listen(wf.id, {
+        'job-start': () => {
+          t.true(didCallCredentials);
+        },
+        'workflow-complete': () => {
+          resolve();
+        },
+      });
+
+      // @ts-ignore
+      engine.execute(wf, {}, { resolvers: { credential } });
+    });
   }
 );
 
@@ -145,7 +155,7 @@ test.serial('listen to events', async (t) => {
   };
 
   const wf = createPlan({
-    id: 'j1',
+    id: t.title,
     adaptors: ['common@1.0.0'],
     expression: 'export default [() => { console.log("x"); }]',
   });
diff --git a/packages/ws-worker/test/reasons.test.ts b/packages/ws-worker/test/reasons.test.ts
index d44430d28..0e1bc797d 100644
--- a/packages/ws-worker/test/reasons.test.ts
+++ b/packages/ws-worker/test/reasons.test.ts
@@ -279,6 +279,26 @@ test('kill: timeout', async (t) => {
   t.is(reason.error_message, 'Workflow failed to return within 100ms');
 });
 
+test('exception: state too large', async (t) => {
+  const plan = createPlan({
+    id: 'x',
+    expression: `export default [(s) => {
+        s.data = new Array(1024 * 1024 * 10).fill("x").join("");
+        return s;
+      }]`,
+  });
+
+  const options = {
+    stateLimitMb: 0.1,
+  };
+
+  const { reason } = await execute(plan, {}, options);
+  t.is(reason.reason, 'kill');
+  t.is(reason.error_type, 'StateTooLargeError');
+  t.truthy(reason.error_message);
+  t.regex(reason.error_message!, /State exceeds the limit/);
+});
+
 test.todo('crash: workflow validation error');
 test.todo('fail: adaptor error');
 test.todo('crash: import error');
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 34a8e6953..7066d0636 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -695,6 +695,9 @@ importers:
       fast-safe-stringify:
         specifier: ^2.1.1
         version: 2.1.1
+      json-stream-stringify:
+        specifier: ^3.1.6
+        version: 3.1.6
       semver:
         specifier: ^7.7.2
         version: 7.7.2