Hedera announced Hedera Agent Kit V4 on May 18, 2026, in its official post, “Hedera Agent Kit V4: Policies, Modular Packages, and Plugin Updates”. The release updates the JavaScript SDK for building AI agents on Hedera and reorganizes the kit into modular @hashgraph-scoped packages. Hedera’s public references include the V4 announcement, the Hedera Agent Kit documentation, the v3-to-v4 migration guide, the plugins documentation, and the GitHub repository.
Breaking changes in the JavaScript SDK
The confirmed breaking changes center on package structure, imports and dependency handling. Hedera’s migration guide says V4 replaces the previous unscoped hedera-agent-kit package with @hashgraph/hedera-agent-kit, while framework integrations now live in separate packages such as @hashgraph/hedera-agent-kit-langchain, @hashgraph/hedera-agent-kit-ai-sdk, @hashgraph/hedera-agent-kit-elizaos and @hashgraph/hedera-agent-kit-mcp. The old npm package will no longer receive updates.
Plugin imports also changed. Built-in plugins are no longer exported from the core package root and must be imported from @hashgraph/hedera-agent-kit/plugins. V4 also changes plugin behavior: an empty plugins array now means the agent has no tools available, while previous behavior may have loaded default tools. Hedera also removed deprecated aliases including coreHTSPlugin, coreSCSPlugin and coreQueriesPlugin.
The Hedera SDK dependency moved from @hashgraph/sdk to @hiero-ledger/sdk. Hedera’s V4 announcement and migration guide state that @hiero-ledger/sdk is now a peer dependency, meaning developers install it directly instead of having it silently pulled in by the Agent Kit package. The migration guide also lists a RETURN_BYTES change, standardizing raw.bytes as Uint8Array.
Functional additions and security boundaries
The main functional additions are hooks, policies and the BaseTool lifecycle. Hedera says V4 lets developers insert logic at four points in a tool’s execution lifecycle, including before execution, after parameter normalization, after the core action and after execution. Policies are TypeScript objects that developers can compose for use cases such as spend limits, address allowlists, audit logging or blocking selected tools.
These are SDK-level controls, not automatic guarantees of security or regulatory compliance. Hedera’s documentation states that older plain-object tools still work in V4, but they do not benefit from hooks and policies unless migrated to BaseTool. A developer still has to define, test and maintain the relevant policies, and any production compliance outcome depends on the application design, operational controls and external review.
V4 also adds or formalizes Google ADK support, standalone MCP tooling and a Hedera x402 facilitator reference implementation. Hedera says the MCP package can be used with MCP-compatible clients, while the x402 reference implementation supports pay-per-request HTTP authorization using HBAR or HTS tokens, with facilitator logic for fee sponsorship and transaction submission.
Fetch.ai and VARA fit only as external context. Fetch.ai’s AEVS focuses on verifiable agent-execution receipts, while Hedera Agent Kit V4 focuses on package modularity, plugin imports, hooks and policy controls. VARA’s rulebooks address regulated virtual-asset activities and disclosure or reserve obligations, not Hedera Agent Kit functionality. Neither reference demonstrates that Hedera V4 provides receipt verification, satisfies regulatory requirements or guarantees secure autonomous-agent behavior.
The confirmed status is that Hedera Agent Kit V4 launched on May 18, 2026, with updated documentation, a public GitHub repository and npm-based package paths for developers. The release introduces breaking changes to package names, imports, plugin loading and SDK dependencies, while adding functional controls through hooks, policies, BaseTool, Google ADK, MCP and x402 tooling.