Phase G in TOGAF provides an architectural oversight of implementation. Implementation Governance ensures that implementation projects conform with the Target Architecture. This short video looks at this in more detail.
The actual development and implementation take place in parallel with Phase G. Phase G makes sure that an implementation project, and also other ongoing projects, are compliant with the defined architectures.
Typically the Target Architecture is developed as a series of transitions to realize business value and benefits as soon as possible, and to reduce risk in a transformation program. Each Transition represents an incremental step towards the Target, delivering business benefits in its own right.
By the time we reach Phase G, the architecture has been developed (in Phases A to D), the opportunities and solutions for delivering the architecture have been identified (in Phase E), and the detailed implementation and migration plan has been finalized (in Phase F). So the role of the architecture team in Phase G is all about providing architectural oversight of the implementation.
This is done by confirming the scope and priorities for deployment, guiding development and solutions deployment, and performing compliance reviews.
An Architecture Contract document is used to drive architecture change. Produced at the beginning of Phase G, and approved by the architecture function and those responsible for implementation, it is the mechanism for assessing compliance in architecture governance.