Why Proxying Claude Code Fails to Replicate the Native Experience: A Technical Deep Dive

Snippet: The degraded experience of proxied Claude Code stems from “lossy translation” at the protocol layer. Unlike native Anthropic SSE streams, proxies (e.g., via Google Vertex) struggle with non-atomic structure conversion, leading to tool call failures, thinking block signature loss, and the absence of cloud-based WebSearch capabilities.

Why Your Claude Code Keeps “Breaking”

When using Claude Code through a proxy or middleware, many developers encounter frequent task interruptions, failed tool calls, or a noticeable drop in the agent’s “intelligence” during multi-turn conversations.

This isn’t a random glitch. As a highly automated agent, Claude Code relies on extreme precision in its underlying data streams. This article breaks down why proxies cannot replicate the native experience across three critical technical dimensions: protocol architecture, “Thinking” signature validation, and cloud-side tool protocols.

1. Protocol Layer: “Lossy Translation” of SSE Streams

The seamless operation of Claude Code is essentially a high-stakes relay of precise data packets. Native Anthropic protocols and proxy solutions (such as Antigravity translating to Google Vertex) have fundamental architectural conflicts.

The Native Mechanism: Precise State Machines

The native Anthropic API utilizes Server-Sent Events (SSE) to deliver fine-grained event streams. It breaks a response into specific, incremental blocks:

  • content_block_start: Defines the type (e.g., text or tool use) and initializes the block.
  • content_block_delta: Provides incremental content updates.
  • content_block_stop: Formally marks the end of the block.

This structure uses index and type tags to form a strict “state machine,” ensuring the agent knows exactly when a tool call begins and ends.

The Proxy Reality: Hard-Coded “Patchwork”

Proxies, particularly those using Google Vertex, face a structural mismatch. Vertex’s API uses a .functionCall object that returns complete tool information at once, lacking the concept of incremental events.

To bridge this, proxies must implement a massive conversion layer. This is not an atomic process; it relies on hard-coded mapping tables and string concatenation to “fake” the native format.

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Technical Risk: If the proxy fails to parse a block—due to missing fields or disordered indices—it triggers error recovery. In tools like Antigravity-Manager, exceeding five parse errors leads to an active disconnection. This is why your session often hangs, requiring a “continue” command to resume.

2. Unstable “Extended Thinking” Signature Passing

“Thinking” blocks represent Claude’s internal reasoning process. This feature is the “brain” of Claude Code, and it is where proxies most frequently fail.

Signature Mismatch

Native Claude uses a signature field to identify the source of thinking content. Proxies must translate between two different formats:

  • Anthropic Format: {"type": "thinking", "thinking": "...", "signature": "..."}.
  • Vertex Format: {"text": "...", "thought": true, "thoughtSignature": "..."}.

Why Proxies Cause “Memory Loss”

During multi-turn dialogues, proxies often struggle to maintain these signatures:

  • Decoding Failures: Vertex may return Base64 encoded signatures. If a proxy fails to decode this correctly and passes a value shorter than 10 characters, it triggers a validation failure.
  • Degradation: When a signature is corrupted during translation, the proxy often downgrades the “thinking” block to a standard “text” block.

The Consequence: Claude Code stops recognizing the content as a reasoning process. In complex tasks, historical reasoning is mismanaged or cleared, causing a significant drop in the agent’s contextual logic and decision-making accuracy.

3. How to Spot a Proxy: The WebSearch Test

The most definitive way to distinguish between native Claude and a proxy is by checking cloud-based capabilities.

WebFetch vs. WebSearch

Feature Mechanism Dependency Proxy Support
WebFetch Model issues tool_use; your local machine makes the HTTP request. Local Network. Supported (as long as the tool instruction is passed).
WebSearch Model issues tool_use; Anthropic’s servers call a search engine. Anthropic Cloud Services. Not Supported.

Why WebSearch Fails on Proxies

  1. Protocol Limitation: Proxies only translate protocols; they do not provide search infrastructure.
  2. API Integration: WebSearch requires paid search engine keys (Google/Bing) integrated at the server level, which Anthropic provides natively but proxies do not.

How-To: Verify Your Claude Interface

You can verify your connection by checking the available tools in your Claude Code environment:

  • Proxy Environment: When asking to search the web, the model will only use WebFetch or return an error stating the tool does not exist.
  • Native Environment: The model successfully invokes the WebSearch tool, leveraging Anthropic’s cloud-side search capabilities.

FAQ: Common Concerns About Claude Proxies

Does using a proxy change the actual model?
The weights of the model (if using a legitimate Vertex-based Claude) remain the same. However, the “lossy translation” of the protocol and the loss of thinking signatures result in a degraded “Agent” experience, leading to logical errors in multi-turn tasks.

Why does my Agent frequently stop and ask me to “continue”?
This is typically due to the proxy layer failing to parse the SSE stream correctly, causing the connection to break or the client to receive incomplete events.

Can third-party clients like OpenCode fix this?
No. The core issue lies in the API endpoint’s non-isomorphic protocol fitting. Whether you use the official CLI or a third-party one, the underlying data loss remains the same if the source is a proxy.