New Foundry - Agent Identity ID and Old Foundry -Agent ID are same ?

No.

They are different identifiers for different objects:

• Old Foundry Agent ID is the agent resource identifier used to reference the created agent.
• New Foundry Agent Identity ID is the identifier for the agent’s Microsoft Entra service principal identity used for authentication and authorization.

The context explicitly separates these concepts:

• Agent ID: service-generated resource ID returned when the agent is created.
• Agent identity: a specialized Microsoft Entra ID service principal that represents the agent at runtime.
• agentIdentityId: the identifier used when assigning permissions to that agent identity.

Also, in the newer model:

• New agents have a non-null agent.identity and therefore a unique identity.
• Legacy agents have agent.identity = null and use the shared project identity.

So the value shown in New Foundry → Entra agent identity → ID should not be treated as the same thing as the old Agent ID like asst_....

A practical way to think about it:

• Use Agent ID to find or call the agent resource.
• Use Agent Identity ID / agentIdentityId to assign RBAC permissions to downstream Azure resources.

• Agent identity concepts in Microsoft Foundry
• Migrate from agent applications to the new agent endpoint and publishing experience
• How can we set agent id prior to creation through YAML File? Is it practically possible to set our own agent id? - Microsoft Q&A