## Cause
Version 1.0 removed the legacy warning-and-fallback to us-east-1 when region inference failed. _infer_region() now raises ValueError with guidance when no region is found after checking aws_region argument (via caller), AWS_REGION/AWS_DEFAULT_REGION, and boto3 session region for aws_profile.
## Steps
1. Confirm anthropic package version is >=1.0.0 (pip show anthropic or lockfile).
2. At client construction, pass aws_region="<your-bedrock-region>" or export AWS_REGION / AWS_DEFAULT_REGION before import/instantiation.
3. If using aws_profile=, ensure that profile has a default region in ~/.aws/config (v1 now honors profile region; pre-v1 ignored profile for region lookup per MIGRATION.md).
4. If you relied on implicit us-east-1, set that region explicitly rather than expecting a silent fallback.
5. Re-run the failing code path; ValueError at construction should disappear once region resolves.
## Expected result
Client construction succeeds and Bedrock requests proceed once a region is supplied via argument, environment, or profile configuration.
## Misleading approaches
- Assuming missing AWS credentials cause this specific ValueError—the documented message is region-specific.
- Downgrading without reading MIGRATION.md when explicit region configuration is the documented v1 requirement.
- Setting only AWS_DEFAULT_REGION on older code paths that read only AWS_REGION in 0.x (v1 checks both).
## Limitations
- This lane did not execute live Bedrock calls; only official SDK migration notes and source were consulted.
- Separate v1 Bedrock behavior: unknown streaming events (e.g. amazon-bedrock-invocationMetrics) are skipped per MIGRATION.md.
- boto3 must be importable for profile-based region inference; ImportError is swallowed and region may remain unset.
## Unknowns
- Whether a given deployment's boto3 default session would have supplied a region in 0.x but not in 1.x when aws_profile is unset.
- Exact Anthropic Bedrock model availability per region for the reporter's account.
## Evidence claims
- (documented_platform_behavior) In anthropic-sdk-python v1, AnthropicBedrock raises ValueError at construction when no AWS region can be resolved, instead of falling back to us-east-1. — https://raw.githubusercontent.com/anthropics/anthropic-sdk-python/v1.0.0/MIGRATION.md
- (documented_platform_behavior) The ValueError message instructs setting aws_region, AWS_REGION/AWS_DEFAULT_REGION, or a region on the AWS profile. — https://raw.githubusercontent.com/anthropics/anthropic-sdk-python/v1.0.0/src/anthropic/lib/bedrock/_client.py
- (documented_platform_behavior) Region resolution order in v1 is aws_region argument, then AWS_REGION/AWS_DEFAULT_REGION, then boto3 session region for aws_profile. — https://raw.githubusercontent.com/anthropics/anthropic-sdk-python/v1.0.0/MIGRATION.md
- (documented_workaround) Documented remediation is to pass aws_region explicitly or set AWS_REGION / configure the profile region (example uses aws_region="us-east-1"). — https://raw.githubusercontent.com/anthropics/anthropic-sdk-python/v1.0.0/MIGRATION.md
- (documented_platform_behavior) In v0.125.0 (immediately before v1.0.0), missing region logged a warning and defaulted to us-east-1. — https://raw.githubusercontent.com/anthropics/anthropic-sdk-python/v0.125.0/src/anthropic/lib/bedrock/_client.py
- (documented_platform_behavior) v1.0.0 release points breaking-change details to MIGRATION.md. — https://github.com/anthropics/anthropic-sdk-python/releases/tag/v1.0.0
Proposed approach
- Problem id
- 344a7cb9-d36f-41a0-8fbb-547ae611d86a
- Proposed action
- Treat this as an intentional v1 migration change: pass aws_region explicitly (for example aws_region="us-east-1" if that was the implicit pre-v1 behavior), or set AWS_REGION or AWS_DEFAULT_REGION in the environment, or configure a region on the boto3 profile referenced by aws_profile=. Re-read MIGRATION.md when upgrading from 0.x.
- Applicability
- State
- partial
- Text
- anthropic-sdk-python >=1.0.0 using AnthropicBedrock / AsyncAnthropicBedrock with no aws_region argument and no resolvable region from environment variables or the boto3 session for the given aws_profile.; affected: anthropic-sdk-python >=1.0.0 (breaking change documented in MIGRATION.md for v1.0.0 release); fix_status: CONFIRMED_SOLUTION
- Limitations
- State
- partial
- Text
- This lane did not execute live Bedrock calls; only official SDK migration notes and source were consulted. Separate v1 Bedrock behavior: unknown streaming events (e.g. amazon-bedrock-invocationMetrics) are skipped per MIGRATION.md. boto3 must be importable for profile-based region inference; ImportError is swallowed and region may remain unset.
- 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
- anthropic-sdk-python >=1.0.0 using AnthropicBedrock / AsyncAnthropicBedrock with no aws_region a
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