Sourced from github.com/modelcontextprotocol/go-sdk's releases.

v1.6.0-pre.1

In this release we introduce several smaller fixes and improvements, and we started working for release 2026-06-30. The main new feature is the introduction of ClientCredentialsHandler for OAuth client credentials grant.

Add ClientCredentialsHandler for OAuth client credentials grant

Added ClientCredentialsHandler implementing auth.OAuthHandler using the OAuth 2.0 Client Credentials grant (RFC 6749 Section 4.4) for service-to-service authentication with pre-registered credentials.

• extauth: add ClientCredentialsHandler for OAuth client credentials grant by @​ravyg in modelcontextprotocol/go-sdk#895

2026-06-30 Release related PRs

• feat: add automatic application_type inference by @​guglielmo-san in modelcontextprotocol/go-sdk#904

  New application_type field is added to the ClientRegistrationMetadata for DynamicClientRegistration. If not specified, the application_type will be inferred from the RedirectURIs. This implements SEP-837.

• feat: HTTP Header Standardization for method and name by @​guglielmo-san in modelcontextprotocol/go-sdk#907

  By mirroring key fields from the JSON-RPC payload into HTTP headers, network intermediaries such as load balancers, proxies, and observability tools can route and process MCP traffic without deep packet inspection, reducing latency and computational overhead. This partially implements SEP-2243.

Behavior Changes

SetError Behavior Change

Previously the SetError method on CallToolResult always overwrote the Content field with the error text. Now SetError preserves the existing value if it has already been populated. You can restore the previous behavior by setting the environment variable seterroroverwrite=1.

• mcp: preserve existing Content in SetError by @​ravyg in modelcontextprotocol/go-sdk#864

Cross-Origin Protection Default Change

Previously (v1.4.1-v1.5.0) default (zero-value) cross-origin protection was applied when CrossOriginProtection in StreamableHTTPOptions was nil. Now cross-origin protection is not enabled by default when CrossOriginProtection is nil. You can restore the previous behavior (enable by default) by setting enableoriginverification=1.

• mcp: remove default cross origin protection by @​maciej-kisiel in modelcontextprotocol/go-sdk#906

disablecrossoriginprotection was replaced by enableoriginverification after the default was changed to not enable cross-origin protection.

jsonescaping option was removed, according to plan.

Other Changes to the SDK

• internal: remove unused util functions by @​alexandear in modelcontextprotocol/go-sdk#871
• build(deps): bump github/codeql-action from 4.32.4 to 4.35.1 by @​dependabot[bot] in modelcontextprotocol/go-sdk#873
• build(deps): bump actions/setup-go from 6.3.0 to 6.4.0 by @​dependabot[bot] in modelcontextprotocol/go-sdk#874
• build(deps): bump actions/setup-node from 6.2.0 to 6.3.0 by @​dependabot[bot] in modelcontextprotocol/go-sdk#875
• build(deps): bump dominikh/staticcheck-action from 1.4.0 to 1.4.1 by @​dependabot[bot] in modelcontextprotocol/go-sdk#872
• oauthex: accept 200 in client registration by @​MatyasVondraOutreach in modelcontextprotocol/go-sdk#877
• mcp: allow Content-Type parameters in streamable transport by @​rafaeljusto in modelcontextprotocol/go-sdk#878
• mcp: preserve existing Content in SetError by @​ravyg in modelcontextprotocol/go-sdk#864
• mcp: fix race condition in ServerSession.startKeepalive by @​begelundmuller in modelcontextprotocol/go-sdk#856
• chore: preserve CNAME when deploying to GitHub pages by @​maciej-kisiel in modelcontextprotocol/go-sdk#884

... (truncated)

• f5f2015 MCPGODEBUG update for 1.6.0 (#893)
• e01639a feat: HTTP Header Standardization for method and name (#907)
• 93a41b2 internal/jsonrpc2: remove unused code (#910)
• 446beae mcp: Upgrade jsonschema-go (#912)
• 2e21834 extauth: add ClientCredentialsHandler for OAuth client credentials grant (#895)
• 2643b22 feat: add automatic application_type inference (#904)
• db50910 mcp: do not re-prompt OAuth after cancelled Authorize (#885)
• 5f2cd8f mcp: preserve transport errors in Write error chain (#888)
• 0edc597 Update README.md (#896)
• 41e1f94 mcp: remove default cross origin protection (#906)
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