Sanitize OpenAI Responses API input to remove base64 encoded images

[Tehnix]

Problem

It seems only some of the API calls had added the sanitazion method for removing base64 encoded images from the input sent to PostHog (see https://github.com/PostHog/posthog-js/issues/2134).

This would currently result in the payload sent to PostHog being too large, giving an error like this:

Error while flushing PostHog: message=HTTP error while fetching PostHog: status=413, reqByteLength=868722, response body=maximum event size exceeded: Event rejected by kafka during send PostHogFetchHttpError: HTTP error while fetching PostHog: status=413, reqByteLength=868722
    at retriable (file:///node_modules/@posthog/core/dist/posthog-core-stateless.mjs:593:77)
    at processTicksAndRejections (node:internal/process/task_queues:105:5)
    at retriable (file:///node_modules/@posthog/core/dist/utils/index.mjs:22:25)
    at PostHog.fetchWithRetry (file:///node_modules/@posthog/core/dist/posthog-core-stateless.mjs:582:16)
    at PostHog._flush (file:///node_modules/@posthog/core/dist/posthog-core-stateless.mjs:549:17) {
  response: Response {
    status: 413,
    statusText: 'Payload Too Large',
    headers: Headers {
      date: 'Wed, 22 Oct 2025 11:03:35 GMT',
      'content-type': 'text/plain; charset=utf-8',
      'transfer-encoding': 'chunked',
      connection: 'keep-alive',
      vary: 'origin, access-control-request-method, access-control-request-headers, Accept-Encoding',
      'access-control-allow-credentials': 'true',
      'x-envoy-upstream-service-time': '17',
      'content-encoding': 'gzip',
      server: 'envoy',
      'strict-transport-security': 'max-age=31536000; includeSubDomains'
    },
    body: ReadableStream { locked: true, state: 'closed', supportsBYOB: true },
    bodyUsed: true,
    ok: false,
    redirected: false,
    type: 'basic',
    url: 'https://us.i.posthog.com/batch/'
  },
  reqByteLength: 868722
}

Most of the work was already done in https://github.com/PostHog/posthog-js/pull/2217, it was just missing the responses API, which this PR adds.

Changes

• Wrapped the input sent to PostHog for the Responses API with sanitizeOpenAI

Release info Sub-libraries affected

Libraries affected

• [ ] All of them
• [ ] posthog-js (web)
• [ ] posthog-js-lite (web lite)
• [ ] posthog-node
• [ ] posthog-react-native
• [ ] @posthog/react
• [x] @posthog/ai
• [ ] @posthog/nextjs-config

Checklist

• [ ] Tests for new code
• [x] Accounted for the impact of any changes across different platforms
• [x] Accounted for backwards compatibility of any changes (no breaking changes!)
• [x] Took care not to unnecessarily increase the bundle size

If releasing new changes

• [ ] Ran pnpm changeset to generate a changeset file
• [ ] Added the "release" label to the PR to indicate we're publishing new versions for the affected packages

[vercel[bot]]

@Tehnix is attempting to deploy a commit to the PostHog Team on Vercel.

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[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week.

[pedsm]

Would love to see this one merged

[Tehnix]

@posthog-bot This is still very much relevant, I'm running a locally patched version of @posthog/ai currently that adds this.

[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week.

[Tehnix]

@posthog-bot This is still very much relevant, I'm running a locally patched version of @posthog/ai currently that adds this.

I'll update the PR to resolve the conflicts tomorrow though

[Tehnix]

@PostHog/team-llm-analytics are you the right team to loop in here? Apologize if I shouldn't tag anyone directly, if that's the case lemme know and I'll just keep the PRs open and let your internal triage handle when you have time for it :)

[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week.

[Tehnix]

@posthog-bot yup, please don't close this!

[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week.

[Tehnix]

@posthog-bot yup, please don't close this!