[its-amann]

Why are these changes needed?

Right now the only way to use Anthropic's fast mode in AG2 is to put speed inside extra_body, which isn't typed or validated. This PR adds a proper speed option ("standard" or "fast") to AnthropicConfig, its copy overrides and CreateOptions. When it's set, the value is sent with both streaming and non-streaming requests. When it's left unset, nothing changes and speed isn't added to the request.

Some models need the fast-mode-2026-02-01 beta header. I didn't add that header automatically, so the caller stays in control of it. The docs now show how to pass it through default_headers, and there are tests checking it works alongside AG2's existing MCP beta header.

Other notes:

• The Anthropic SDK minimum goes up to 1.15.0, since that's the first version with a public speed argument. uv.lock is updated to match.
• I left Usage unchanged. It only adds up token counts, so a per-request speed label doesn't really fit there.

Tested on Python 3.12 with Anthropic SDK 1.15.0:

• just test: 4,382 passed, 103 skipped, 329 deselected, 2 xfailed. This is the non-LLM run, not the full CI matrix.
• Anthropic unit tests: 284 passed, 1 skipped, 1 xfailed, including 14 new tests for speed.
• Ruff lint/format and strict mypy pass on the Anthropic modules.
• Wheel and sdist build fine.

Related issue number

Closes #3489

Checks

• I've included any doc changes needed for https://docs.ag2.ai/. See https://docs.ag2.ai/latest/docs/contributor-guide/documentation/ to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

AI assistance

I used AI assistance for parts of the implementation, the tests and this description.

• I understand the changes in this PR and can explain them in my own words.
• I have verified that the PR description accurately reflects the actual diff.
• If AI assistance was used, I reviewed, tested, and validated the generated code/text before submitting.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
ag2/config/anthropic/anthropic_client.py	81.05% <100.00%> (+7.99%)	⬆️
ag2/config/anthropic/config.py	91.66% <100.00%> (+0.62%)	⬆️

... and 13 files with indirect coverage changes

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