An SDK upgrade can change an agent even when the application code does not.
OpenAI Agents SDK 0.20.0 changes the implicit default model to gpt-5.6-luna. Explicit models, run-level overrides, and OPENAI_DEFAULT_MODEL still take precedence, but an application that relied on the implicit default will change runtime behavior by upgrading the dependency alone.
The release also crosses the MCP v2 migration boundary. Local connections support MCP Python SDK v1 and v2 across stdio, SSE, and Streamable HTTP. Custom HTTP authentication and client factories still need to use the HTTP types owned by the installed MCP major version, or pin mcp<2 while migrating.
Two more changes belong in the recovery test: RunState.add_input() can persist new input before a resumed model call, and tool approvals are bound more tightly to concrete invocation identity.
This is a release-note read, not a local reproduction. Before upgrading, pin the model ID, Agents SDK version, MCP major, transport, approval call ID, and one interrupt-resume canary.
Official release: https://github.com/openai/openai-agents-python/releases/tag/v0.20.0
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