tidb-cloud: add description for Starter agent plan (#22877)

Author: lilin90

tidb-cloud/architecture-concepts.md

@@ -42,7 +42,8 @@ TiDB Cloud makes it easy to scale your database, handle complex management tasks
 
 The Starter plan is ideal for those who are getting started with TiDB Cloud. It provides developers and small teams with the following features:
 
-- **No cost**: This plan is completely free, with no credit card required to get started.
+- **No cost**: This plan is free when usage is within the [free quota](https://www.pingcap.com/tidb-cloud-starter-pricing-details/). No credit card is required to get started.
+
 - **Storage**: Provides an initial 5 GiB of row-based storage and 5 GiB of columnar storage.
 - **Request Units**: Includes 50 million [Request Units (RUs)](/tidb-cloud/tidb-cloud-glossary.md#request-unit-ru) for database operations.
 

tidb-cloud/branch-overview.md

@@ -41,6 +41,10 @@ Currently, TiDB Cloud branches are in beta and free of charge.
 
 - For each organization in TiDB Cloud, you can create a maximum of five branches by default across all {{{ .starter }}} and Essential instances. The branches of a {{{ .starter }}} or Essential instance will be created in the same region as the instance, and you cannot create branches for a {{{ .starter }}} or Essential instance that is throttled or larger than 100 GiB.
 
+    > **Note:**
+    >
+    > For paid organizations building agent platforms or other services that require a large number of branches, TiDB Cloud offers the **Instance Capacity Plan**, which lets you create more than five branches. To learn more, see the [Instance Capacity Plan](/tidb-cloud/select-cluster-tier.md#instance-capacity-plan).
+
 - For each branch of a free {{{ .starter }}} instance, 10 GiB storage is allowed. For each branch of a {{{ .starter }}} instance with spending limit > 0, 100 GiB storage is allowed. Once the storage is reached, the read and write operations on this branch will be throttled until you reduce the storage.
 
 - Branches are intended for short-term feature development and functional testing. Because branches lack auto-scaling capability, they are not suitable for performance testing.

tidb-cloud/select-cluster-tier.md

@@ -25,7 +25,8 @@ TiDB Cloud Starter is a fully managed, multi-tenant TiDB offering. It delivers a
 
 The free plan is ideal for those who are getting started with {{{ .starter }}}. It provides developers and small teams with the following essential features:
 
-- **No cost**: This plan is completely free, with no credit card required to get started.
+- **No cost**: This plan is free when usage is within the [free quota](https://www.pingcap.com/tidb-cloud-starter-pricing-details/). No credit card is required to get started.
+
 - **Storage**: Provides an initial 5 GiB of row-based storage and 5 GiB of columnar storage.
 - **Request Units**: Includes 50 million [Request Units (RUs)](/tidb-cloud/tidb-cloud-glossary.md#request-unit-ru) for database operations.
 
@@ -45,6 +46,16 @@ Once a {{{ .starter }}} instance reaches its usage quota, it immediately denies
 
 To learn more about the RU consumption of different resources (including read, write, SQL CPU, and network egress), the pricing details, and the throttled information, see [{{{ .starter }}} Pricing Details](https://www.pingcap.com/tidb-cloud-starter-pricing-details/).
 
+### Instance Capacity Plan
+
+For each organization in TiDB Cloud, you can create a maximum of five [branches](/tidb-cloud/branch-overview.md) across all {{{ .starter }}} and Essential instances by default.
+
+For each paid organization in TiDB Cloud, you can create up to 100 {{{ .starter }}} instances and branches in total, with each branch counted as a separate instance.
+
+For paid organizations building agent platforms or other services that require a large number of instances and branches, TiDB Cloud offers the **Instance Capacity Plan**. With this plan, each paid TiDB Cloud organization can create more than five branches and is not subject to the limit of 100 {{{ .starter }}} instances and branches. To learn more and apply for the Instance Capacity Plan, fill out the [application form](https://www.pingcap.com/programs/agentic-ai-instance-capacity).
+
+You will receive an email notification once your application for the TiDB Cloud Instance Capacity Plan is approved. 
+
 ## {{{ .essential }}} {#essential}
 
 For applications experiencing growing workloads and needing scalability in real time, the Essential plan provides the flexibility and performance to keep pace with your business growth with the following features: