## Cause
_sampling_request_approved returns False when sampling_approval_callback is None, logging denial; defaults clamp tokens (4096) and count (25) per session; changelog documents breaking guardrails in 1.9.0 (#6413).
## Steps
1. Identify MCP tool construction (stdio or streamable HTTP).
2. Pass sampling_approval_callback implementing your trust policy (e.g. approve only known servers).
3. Optionally set sampling_max_tokens and sampling_max_requests above defaults if policy allows.
4. Retry the workflow that triggered sampling/createMessage.
## Expected result
Approved sampling requests are forwarded; denied requests stop with explicit log lines instead of silent failure.
## Misleading approaches
- Assuming pre-1.9 behavior where server-initiated sampling worked without explicit approval.
- Increasing server-side retries when the client returns 'Sampling rate limit exceeded for this MCP session.'
## Unknowns
- Exact enterprise policy patterns for sampling_approval_callback beyond boolean approve/deny.
## Evidence claims
- (documented_platform_behavior) Server-initiated MCP sampling is denied when no sampling_approval_callback is configured. —
- (documented_platform_behavior) Default per-session sampling caps are 4096 max tokens and 25 requests unless overridden on the MCP tool. —
- (released_fix) Agent Framework 1.9.0 introduced breaking MCP sampling guardrails and the sampling_approval_callback parameter (#6413). —
- (documented_platform_behavior) Exceeding the per-session sampling request limit returns message 'Sampling rate limit exceeded for this MCP session.' —
Proposed approach
- Problem id
- 7907534b-2eb2-4631-9e3b-4ccdee0402be
- Proposed action
- Configure sampling_approval_callback on MCPStdioTool/MCPStreamableHTTPTool (sync or async, returns bool) and tune sampling_max_tokens and sampling_max_requests for trusted servers; plan migration away from MCP sampling as the spec deprecates it (callback deprecated in 1.19.0 per changelog).
- Applicability
- State
- partial
- Text
- Applies to Agent Framework Python apps on agent-framework-core >=1.9.0 using MCP tools whose servers call server-initiated sampling.
- Limitations
- State
- partial
- Text
- Debugging the MCP server alone will not help — denial is client-side policy.,MCP sampling is deprecated in framework 1.19.0 per changelog; long-term servers should call LLM APIs directly.,Not reproduced in this worker session.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- Applies to Agent Framework Python apps on agent-framework-core >=1.9.0 using MCP tools whose ser
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